The field of photovoltaics (PVs) is primarily concerned with maximizing the conversion efficiency of photon energy into electrical energy under the constraint of minimum cost. The resulting figure of merit of a given photovoltaic technology is therefore cost per Watt. Therefore, some of the driving forces for innovation in PVs comprise increasing the efficiency of the solar cell device (or system), decreasing materials costs, or decreasing processing costs. Additionally, the industry is looking to increase the versatility of photovoltaic (PV) materials to address other market needs. An example of this is integrating flexible solar cells into architectural or structural materials or other non-standard solar panel applications. Although efforts have been made to develop this technology, the materials used do not permit high efficiency energy conversion. For these reasons, there remains a need for a method of fabricating low-cost, high efficiency PV substrates that can be used to 1) increase the cost per Watt value of conventional PV technology or 2) permit fabrication of novel, high-efficiency PV materials that are flexible and can be used to produce new PV products.
The related art describes various methods for producing thin film materials used in the manufacture of PVs, or similar devices by various methods such as peeling, e.g., Shimoda, et al., U.S. Pat. No. 6,887,650; Iwane, et al., U.S. Pat. No. 6,682,990; Mizutani, et al., U.S. Pat. No. 6,802,026; Nagakawa, et al., U.S. Pat. No. 6,452,091; Seki et al. U.S. Pat. No. 5,000,816; and Sumi., U.S. Pat. No. 4,855,012.
A different technique has been used recently [F. Dross et al., Appl. Phys. A, 89 (2007) p. 149] to fabricate a thin single-crystal Si layer from a thicker source substrate using the “spontaneous” spalling resulting from thick Ag and Al bi-layers and high temperature annealing to create tensile strain through thermal expansion mismatch. The problem with this approach is twofold; first, the high temperature step limits the ability to integrate partially (or fully) processed PV devices (devices with formed dopant junctions or metallization) with the spalling process (due to excessive dopant diffusion and incompatibility of most metals with high temperature) and adds cost to the materials; and second, spontaneous spalling leads to poorly controlled fracture, physical curling of the stressor layer/exfoliated semiconductor layer combination, and the requirement for very thick stressor layers to self-initiate fracture in the substrate.